December 4, 2022


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Microsoft announces progress on a completely new type of qubit

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Microsoft announces progress on a completely new type of qubit

Image of a graph with two clear peaks.
in great shape , Microsoft says it sees two clear peaks at the ends of the wire, with a good energy separation between those and any other energy states.

So far, two primary quantum computing technologies have been commercialized. One type of hardware, called a transmon, consists of superconducting wire loops connected to the resonator; It is used by companies such as Google, IBM and Rigetti. Companies such as Quantinum and IONQ have instead used individual ions placed in the light trap. At the moment, both technologies are in a strange place. They have clearly been demonstrated to work, but they require some significant scaling and quality improvement before useful calculations can be made.

It may come as little surprise to see that Microsoft is committed to an alternative technology called “topological qubits.” This technology lags far behind the company’s other options just announced It has worked on physics to form an orbit. To better understand Microsoft’s vision, Ars spoke to Microsoft engineer Chetan Nayak about the company’s progress and plans.

one qubit. foundation of

Microsoft is lagging behind some competitors because the basic physics of its systems were not fully explored. The company’s system relies on controlled production of a “majorana particle”, something that had only been demonstrated to exist within the last decade (and even then, its discovery has led to the creation of a “majorana particle”). been controversial,

The particle gets its name from Ettore Majorana, who proposed the idea back in the 1920s. In simple words, a Majorana particle is its own antiparticle; Two Majorana particles that differ in their spin will annihilate if they meet. So far, none of the known particles appear to be Majorana particles (not all neutrinos are, of course). But the concept is permanent because of the possibility of creating Majorana quasiparticles, or a collection of particles and fields, which in some contexts behave as if it were a single particle.

The most prominent quasiparticle is probably the Cooper pair, in which two electrons pair up in a way that changes their behavior. Cooper pairs are necessary to get superconductivity to work.

Nayak said Microsoft’s system consists of a superconducting wire and its attendant Cooper pairs. Under normal circumstances, having an extra, unpaired electron fixes the total energy cost of the system. But in a sufficiently small wire in the presence of a magnetic field, it is possible to stick an electron at the end of the wire without any energetic cost. “In a topological state and a topological superconductor, you have states that can adsorb an extra electron, without energy cost,” Nayak told Ars.

This being quantum mechanics, the electron is not localized to the end of the wire where it is inserted; Instead, it is delocalized to both ends. “The two ends are basically the real and imaginary parts of that quantum wave function,” Nayak said. These final states are called Majorana zero modes, and Microsoft is now saying it has created them and measured their properties.

Quasiparticle to Qubit. As far as

By themselves, Majoranas are not usable as zero mode qubits. But Nayak said it is possible to connect them to a nearby quantum dot. (Quantum dots are pieces of a material the size of a material so that they are smaller than the wavelength of an electron in that material.) He described a U-shaped wire with Majorana zero modes at each end and the proximity to a quantum dot. ends in.

“You can have an electron tunnel from the quantum dot to one Majorana zero mode and one electron tunnel from the other Majorana zero mode, effectively as a virtual process,” Nayak told Ars. These exchanges alter the quantum dot’s ability to store charge (its capacitance, in other words), a property that can be measured. Nayak also said that the connection between the wire and the quantum dots could be controlled, potentially allowing the Majorana zero mode to be disconnected, which would help preserve their state.

Microsoft hasn’t been in a position to add the quantum dot. But it has taken a considerable amount of work to work the topological state into the wire. The materials the company is using are relatively uncommon: aluminum as the superconducting wire and indium arsenide as the semiconductor around it. Microsoft is making all the devices itself.

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